The invention generally relates to the art of establishing connections in a network; and more specifically to the establishment of a virtual circuit in an asynchronous transfer mode (ATM) network using an operator-directed routing path.
A permanent virtual circuit (PVC) provides a bearer channel path across a network which comprises a series of bearer channel links that are interconnected by xe2x80x9cpermanentxe2x80x9d bearer channel cross-connections established on network nodes under the direction of a central network management authority. This authority can be a human operator which decides the route and manually configures each cross-connection individually through a network management terminal interface (NMTI). Alternatively, the authority can be a network management system (NMS), which automatically selects the route through the network according to some algorithm or objective when requested by one or more human operators. The NMS is connected to each network node typically through an independent control channel and thereby automatically establishes the cross-connections.
For each PVC thus established, the central network management authority can choose a route through the network which meets criteria based on network-wide policies rather than single-element policies. One example of a network-wide routing policy is a policy of using the most efficient route through the network, for example, by minimizing the number of network nodes traversed; or by minimizing the cumulative costs of links which are traversed; or, by balancing the number of traversed nodes and the cost of the traversed links. Another example is balancing network usage across different network nodes, or the links between network node, such that no one network node or link is carrying a large proportion of all PVCs traversing the network.
This approach to establishing connections provides various benefits. For instance, since there is only one central network management authority, i.e. an expert human network operator or a powerful computer running sophisticated network management software, the cost of provisioning the authority is inexpensive relative to the overall cost of the network. In addition, whenever network management policy is changed with respect to the routing of circuits or connections, it is easy to implement the policy changes because they only need to be made in one place, in the central management authority.
This approach also has various shortcomings. One shortcoming is the relatively high cost of maintaining an exact and up-to-date picture of network conditions in the central network management authority in order to enable routing and re-routing decisions to be made with accuracy. Another shortcoming is the slow speed at which the central network management authority can re-route PVCs in the event of a network failure. This is due to the time required for the central authority to (i) become aware of the network failure, (ii) find new routes through the network for all affected PVCs which satisfy all of the various network element and network-wide criteria, and (iii) re-establish all affected PVCs along the chosen routes.
A soft permanent virtual circuit (SPVC) provides a bearer channel path across a network which comprises a series of bearer channel links that are interconnected through xe2x80x9cswitchedxe2x80x9d (i.e. on-demand) bearer channel cross-connections made across a series of network nodes. More specifically, the ingress and egress network nodes are provisioned by an operator (either through the NMTI or NMI) but the cross-connects are commissioned via signalling, like a switched virtual connection (SVC), as the SPVC is signalled and routed across the network from the ingress network node to the egress network node. An SVC is a path that is signalled from user side UNI to user side UNI whereby the route is chosen by the network nodes as the path is signalled from a source end station towards a destination end station. The individual cross-connects for the SVC path are configured and connected by call control software running on each node along the path as the path steers itself through the network using routing tables resident on each node (i.e., hop-by-hop routing) or according to a predetermined route specified in the connection request (i.e., source-routing). Thus, SPVCs are a kind of hybrid between PVCs and SVCs since SPVCs, like PVCs, are initiated by the central network management authority and require no UNI signalling between the user and the network, but, like SVCs, the cross-connects are routed through the network and maintained by the network nodes themselves.
One of the benefits of this approach to establishing connections is that SPVCs can be re-routed more efficiently because the network nodes which are closest to a network failure can quickly detect the failure and initiate the re-routing procedures. Hence, the virtual circuits can be re-established more quickly and at less cost than PVCs can be reestablished by a central network management authority. Indeed, it is estimated that SPVCs improve the cult restoration re-route performance for connections by an order of magnitude because the processing is distributed within the network rather than being centrally managed by the NMS.
The are also various disadvantages with this approach. First, it is not possible for an expert human operator to intervene and influence the network nodes to use routes for an SPVC through the network that differ from the mutes that would be automatically chosen by the network nodes, or to modify routes chosen automatically by the network nodes, for example, in order to impose routing criteria for which the network nodes have not been designed or configured. Second, due to the large number of network nodes, it is difficult and costly to employ powerful computing devices for each network node; therefore, the sophistication of the routing algorithms implemented by the network elements cannot, at reasonable expense, approach the sophistication of the routing algorithms that can be implemented by a central network management authority which comprises of a smaller number of computing devices. Third, again due to the large number of network nodes, it is difficult and costly to upgrade or reconfigure each network node whenever a network-wide policy has changed with respect to the routing and re-routing of virtual circuits, for example, when a new virtual network has been created out of available resources on many different nodes across the network, or when network management policies change with respect to the weighting of different criteria such as the number of nodes traversed versus cumulative cost of links traversed.
To further elaborate upon the disadvantages provided by both PVCs and SPVCs, consider for example, the reference network shown in FIG. 1. A customer wishes to connect end station or customer premise equipment (CPE) 20 from Toronto to Montreal, and purchases two (2) connections or virtual circuits 24a and 24b therebetween to ensure redundancy. If the connections 24a and 24b between Montreal and Toronto are established using SPVCs, then, since the path, i.e. intermediate nodes 28 and links 26, of the connections are not preconfigured, a situation such as illustrated in FIG. 1 could occur, wherein the network nodes select the shortest path between the CPEs. Thus, the paths of both connections 24a and 24b are identical, traversing node A, link 26ag, node G, link 26dg, and node D. This result would thus destroy the sought after redundancy. In order to ensure that the path of each connection does not follow a common link or share the same physical interface of the other, it is possible to provision the connections as PVCs in order to manually configure the cross-connections and predetermine the followed links. However, this strategy brings with it the above described disadvantages of PVCS, in particular, the relatively slow re-route performance of the centralized NMS in the event of a service disruption such as a failed link. For customers who have demanding maximum permissible service disruption requirements, e.g., one second per year, the re-route performance of PVCs by the NMS is unacceptable. For example, it may take the NMS two hundred (200) seconds to re-route a severed OC-3 cable carrying ten thousand (10,000) connections at fifty (50) re-routes per second.
Similar problems arise in router based network environments such as those networks which employ tag switching or multi-protocol label switching (MPLS).
The invention seeks to avoid various limitations of the prior art by providing a hybrid type of connection which features the fast, distributed processing re-route capabilities of SVCs or SPVCs, yet enables a human operator to direct the routing of the path across the network like a PVC. Broadly speaking, one aspect of the invention relates to a communications network comprising a user interface means for enabling a human operator to manually provision a predetermined preferred path across the network, which path comprises a source network element, a destination network element, as well as intermediate network elements and, optionally, the intermediate ports or links between these network elements. The user interface means is connected to the source network element which encapsulates the manually provisioned preferred path in a source-routed connection request message that is signalled to the network elements along the preferred path. The network elements include call processing means to ensure that the manually routed connection traverses these intermediate nodes and the specified intermediate links as the connection request is signalled from the source network element to the destination network element.
In a first aspect, a method of establishing a connection between a source network element and a destination network element in a communications network is provided. The source network element is associated with a path selection algorithm for identifying network path elements that define the connection. The method includes:
(a) providing an operator selected preferred routing indication to the source network element, the preferred routing indication defining at least one preferred network path element of the connection located between the source network element and the destination network element;
(b) providing an operator selected re-routing indication, the re-routing indication defining instructions for re-establishing the connection in the event at least one preferred network path element defined by the preferred routing indication becomes unavailable for sustaining the said connection;
wherein the preferred routing indication is used to establish the connection instead of corresponding network path elements identified by the path selection algorithm of the source network element.
The preferred routing indication and the re-routing indication may be originated externally of the source network element, and the re-routing indication may be provided to the source network element. The re-routing indication may include a direction to re-establish the connection using the preferred routing indication.
The method may further include creating a source-routed connection request message which specifies the preferred routing indication, and the source-routed connection request message may be signalled to the destination network element so as to establish the connection.
The communications network may further include a network management element for originating the preferred routing indication, and the source network element may create the source-routed connection request message.
The intermediate network element may be one of a subnetwork, a network node, and a link between two adjacent network elements that are located between the source network element and the destination network element.
The preferred routing indication may be manually predetermined.
The method may further include, establishing a bearer channel cross-connection on each network path element which constitutes a network node in order to connect any two adjacent network elements of the source network element, the destination network element and any network element therebetween which is located along the network path elements that define the connection.
A network path element may include at least one link between two adjacent network elements of the source network element, the destination network element and the network element therebetween that is located along network path elements that define the connection, and the source-routed connection request message specifies the link.
Every two adjacent network elements which constitute network nodes and which correspond to each link may commission a bearer channel cross-connection thereon so as to utilize each link in establishing the connection.
Adjacent network elements of the source network element, the destination network element and each network element therebetween which is located along network path elements that define the connection may automatically select any available link in the event the preferred routing indication does not identify a link to be used therebetween.
The re-routing indication may be stored at the source network element.
The re-routing indication may include at least one alternate path indication each defining at least one network path element of the connection located between the source network element and the destination network element, the alternate path indication not being identical to the preferred routing indication.
The re-routing indication may include a direction to re-establish the connection selected from one of (i) using the preferred routing indication; (ii) using at least one alternate path indication each defining at least one network path element of the connection located between the source network element and the destination network element, each alternate path indication not being identical to the preferred routing indication; (iii) using any possible path from the source network element to the destination network element; and (iv) using each alternative path indication successively if an earlier used alternative path indication becomes unavailable for sustaining the connection, and if every alternative path indication becomes unavailable as aforesaid, then using any possible path from the source network element to the destination network element.
The communications network may be a P-NNI network and the any possible path may be determined using P-NNI routing techniques.
The source-routed connection request message may be one of (i) an SPVC call setup message; and (ii) an SVC call setup message; which includes a designated transit list (DTL) specifying each preferred network path element of the connection.
The method may further include, cranking back the source-routed connection request message to the source network element for re-routing the connection in the event that any of the at least one link is inoperative during establishing of the connection.
The method may further include, signalling the source network element to re-route the connection in the event that any of said at least one link becomes inoperative after establishment of the connection.
The manual predetermination of the preferred routing indication may be indicated by one of: manually entry; manual with point and click assistance; and automatic route generation with optional manual editing.
ODR SPVCs, having paths provisioned by a human operator, offer the same services as the prior art SPVCs, and provide various other additional benefits. For instance, ODR SPVCs allow the operator to deliberately control the distribution of connections across a network, Additionally, the operator can include or exclude certain nodes(s) from the path of an ODR SPVC for security reasons. For example, a connection may need to traverse certain nodes to ensure the connection is protected from unauthorized access. This offers some degree of information security for the customer. In addition, the operator can setup ODR SPVCs to ensure a network failure will not disrupt all of a customers connections by requiring a certain portion of the customers connections to traverse a certain path while the remainder traverse completely unrelated path(s). If any path(s) experiences failure, the failure would not disrupt all of the customer""s connections. Furthermore, ODR SPVCs can be provisioned across a network to ensure that the network is efficient. For example, the operator can direct certain ODR SPVCs to traverse the network over the least amount of hops, thereby guaranteeing that a connection will take the most direct path to its destination. The operator may even direct ODR SPVCs to avoid certain nodes to free up resources and avoid congestion in those nodes.